Design Of Thermostable Strongly Basic Resin With Guanidyl Group And Study On Its Performance

Strongly basic anion exchange resin is widely used in water treatment, electric power industry, the separation and purification of biological and chemical agents, as well as catalytic synthesis. However, the temperature range in which conventional strongly basic anion exchange resin, especially in the form of hydroxyl group as counter ion can be applied has an upper limit of60℃due to the resin’s low thermal stability in water. This phenomenon arises as a result of the structure of quaternary ammonium group through the reaction of chloromethylated resin with tertiary amine. The resin having quaternary ammonium group suffers from Hofmann degradation at higher temperatures, leading to the desquamation or conversion of strongly basic groups attached to the polymeric matrix. Therefore, the application of strongly basic anion exchange resin is greatly limited. At present, many efforts have been devoted to improving the thermal stability of polymeric resins by modification of the linkage between the quaternary ammonium groups and the polystyrene. However, it has been concluded that such modifications would not be economical for application to large-scale preparations because of the complicated synthetic processes required. Moreover, although these methods lead to slight improvements, it is difficult to fundamentally enhance the thermal stability due to the inherent nature of the quaternary ammonium group.Small molecule guanidine has the advantage of strong alkalinity, high thermal stability, special chemical structure, which has been applied to immobilize onto the resin innovatively through two different methods (namely direct immobilization and the in situ reaction) to afford novel guanidine resin. In the thesis, the thermal stability of the guanidine resin synthesized was studied in detail, for the first time, summing up the rule between thermal stability and the connection mode. The resin synthesized changed the influence of quaternary ammonium groups on the thermal stability of resin, improving the thermal stability of the strong-base anion exchange resin. The applications of guanidine resin both as adsorbent in lentinan decoloring process and as catalyst in catalyzing Knoevenagel condensation reaction were also investigated. The main research contents and conclusions are as follows:Part I:The connection mode between thermal stability and guanidine groups was study for the first time. The guanidine resins were prepared by the nucleophilic substitution reaction of free guanidine and gel chloromethylated resin as the raw material. The guanidine resins were characterized by FT-IR, TQ and the contents of the basic functional groups bound to the resin were determined by acid-base titration and elemental analysis. The reaction conditions were optimized. It was shown that the thermal stability of the resin was inversely proportional to the amounts of guanidine groups attached on the resin, which was confirmed by thermogravimetric analysis. The more stable guanidine resin was, the lower contents of guanidine resin were. It can be attributed to the unique structure of guanidine and the cross-linking connection mode between the guanidine and the polymeric matrix. According to the explanation to the result, p-xylylene dichloride (XDC) was selected as a post-synthesis cross-linking agent to react with guanidine incorporated into the resin in order to improve thermal stability of resin with high contents of guanidine groups. The experiment result was demonstrated that the thermal stability of resin had been improved, which verified the above explanation in the meanwhile. The adsorption performance of guanidine resin and guanidine-XDC resin were both studied. The benzoic acid and methyl orange were selected as adsorbates. Experimental results were showed that the isotherms could be represented by Freundlich model reasonably. The adsorption mechanism indicated that the adsorption was the synergistic effect of hydrophobic interaction, dipole-dipole interaction and hydrogen bonding.Part II:To obtain a thermally stable resin with high contents of guanidine groups loaded, gel benzylamine polystyrene had been allowed to react nucleophilic addition with cyanamide or thiourea in situ to generate strongly basic resin from weak basic one, followed by the reaction with p-xylylene dichloride (XDC) to give guanidine-XDC resin. The resins synthesized were determined by FT-IR, acid-base titration, elemental analysis and SEM. The effects of pH value, material ratio and temperature on the reaction were also investigated. The experiment results had been indicated that the resin had good thermal stability. At the same time, different types of guanidine resins were prepared by the reaction of the resins having different matrixes, as raw materials, with free guanidine.Part III:The guanidine resin as the adsorbent was, for the first time, applied in lentinan decoloring process. The macroporous guanidine-XDC resin had been prepared through the one-step reaction of primary amine resin with cyanamide, followed by the reaction with p-xylylene dichloride (XDC) to obtain macroporous resin with guanidine groups. The resins synthesized had been characterized by acid-base titration, elemental analysis, SEM and N2adsorption-desorption experiments. Under the same conditions, guanidine resins, commercial cation exchange resins, commercial anion exchange resins, macroporous resins were screened to carry out the decolorization of lentinan. It was shown that guanidine-XDC resin had the best decoloring efficiency, which had been explained using the corresponding principle. The static adsorption experiments of the lentinan on guanidine-XDC resin were performed under different temperature, amounts of the resin, pH value, and were set up the adsorption thermodynamics model. Besides, the technology on the decolorization of lentinan were studied.Part IV:The Knoevenagel condensation reaction catalyzed by gel guanidine-XDC resin as heterogeneous catalyst had been investigated for the first time. The effect of reaction temperature, amounts of the resin, ratio of reactants, reaction solvent, reaction time, reaction selectivity, reusability on the Knoevenagel condensation reactions between cyclohexane and ethyl cyanoacetate were also discussed. The catalytic mechanism had been proposed. The guanidine-XDC resin had been found to efficiently catalyze Knoevenagel condensation reactions with the yield of83.1-95.3%, and even the reactions of relatively inactive substrates can be accomplished at higher temperatures. The resin can be removed after reaction by simple filtration with the advantages of easy separation, mile reaction condition, recyclability without losing catalytic activity more than7times. All the reaction products were characterized by NMR, FT-IR, MS, GC, which were consistent with the literature results.